The study in questioned injected mice with a certain molecule named GW501516, increasing the expression of a receptor called PPARd that trains our muscles to burn fat over glucose when exercising. Without any kind of training, the injected mice ran roughly 100 minutes longer than normal mice.

"When we think about exercise and the metabolic benefit of exercise, we think of a few mechanisms… more mitochondria, fiber type shifting from fast- to slow-twitch fibers, enhanced fat metabolism,” Barnes, who was not involved in the study, explained to Discover Magazine. "This study suggests that PPARd affects the muscle’s fuel selection, namely by preferentially burning fat and sparing glucose, without relying on increased mitochondria or slow twitch fibers. The genes activated by PPARd or the GW agonist all appear to be related to enhanced fat metabolism.”